Question

In a synthesis experiment you obtain a sample of product on which you do a melting point determination and find a melting point range of 108.0 to 114.3 degrees Celsius. The sample is supposed to be benzoic acid. What preliminary conclusion(s) can you reach from this one determination? (select true or false)
1) The sample is probably impure.
2) The sample is not benzoic acid
3) The melting point determination may need improvement -- it may not have been done properly, and make sure it was repeated at least once.
5) The sample probably needs recrystallization.
6) The sample may be benzoic acid.

Answer 1

Answer:1) the sample is probably impure

Explanation:this is because pure samples have sharp melting points. If the sample is suppose to be benzoic acid, and the melting point of pure benzoic acid is 122.3oC, then it is definitely impure. The presence of Impurities lowers melting points of purr substances through melting points depression. So the sample is impure benzoic acid. You also have to calibrate the thermometer before taking measurements.

Answer 2

Answer:

1) The sample probably needs recrystallization.

2) The sample may be benzoic acid.

3) The sample is probably impure.

4) The melting point determination may need improvement -- it may not have been done properly, and make sure it was repeated at least once.

Explanation:

Hello,

In this case, as the obtained range for the melting is lower than the pure benzoic acid's melting point which is 122.3 ºC one can state the following preliminary conclusions:

1) The sample probably needs recrystallization: this is a suitable technique to increase a sample's purity, therefore, the further melting point will be determined more precisely.

2) The sample may be benzoic acid: since the range is slightly close to the pure benzoic acid's melting point, probably, by increasing the sample's purity, it could be substantiated it is benzoic acid.

3) The sample is probably impure: as the obtained range is lower than the real benzoic acid's melting point, the estimated range could be affected by the samples impurity by lowering its value.

4) The melting point determination may need improvement -- it may not have been done properly, and make sure it was repeated at least once: errors during experimental measurements are quite normal, therefore, a repetition could be performed in order to verify the previous determined data.

Best regards.